Normal keratinocytes undergo differentiation in vitro in a manner regulated by calcium. Cytokines, tumor necrosis factor - alpha (TNF) and interferon- gamma (IFN) (which have receptors on keratinocytes), and the steroid hormone, 1,25 dihydroxy vitamin D3 [1,25(OH)2D], (which is produced by keratinocytes) promote the differentiation of normal keratinocytes, probably through calcium dependent mechanisms. Squamous carcinoma cell lines (SCC lines) show remarkable fidelity in their genotype to normal keratinocytes, but exhibit different degrees of differentiation in vitro. Some SCC lines remain in their proliferative stage of growth and cannot be induced to differentiate by calcium. In this proposal we address the question whether SCC lines respond to the prodifferentiating effect of 1,25(OH)2D, TNF and IFN, and whether the failure of SCC lines to differentiate normally is due to a defect in the calcium dependent intracellular molecular mechanisms by which these agents regulate differentiation.